Hi, all,
I have two questions to bother you.
the first one is: Here is part of the model I defined. It is Heisenberg AFM model with different coupling constant J on each type of bond. See the defined BONDTERM. The default coupling Jz2 is J, and I specify J=1 in the parameter file.
<HAMILTONIAN name="spin"> <PARAMETER name="Jz" default="J"/> <PARAMETER name="Jxy" default="J"/> <PARAMETER name="J" default="1"/>
<BONDTERM type="2" source="i" target="j"> <PARAMETER name="Jz2" default="J"/> <PARAMETER name="Jxy2" default="J"/> Jz2*Sz(i)*Sz(j)+Jxy2*exchange_xy(i,j)+ ........
However, when I tried to run it, I got following error message.
parsing task files ... Starting task 1. Cannot evaluate expression Jz2 * -0.5 * -0.5
It seems that Alps didn't take the numerical value of Jz2. Or I make a mistake somewhere. Can someone help point out?
The second question about "sparse diagonalization":
When I use Lanczos method to get the ground state energy, it seems that it can only give me the value of energy, not the degeneracy of states. The value of energy has error in it, as a result, sometimes, it will consider two degenerate states as two different states. Is my understanding correct?
So, in order to judge whether the two states are degenerate or not from the energy value, we need to estimate of the magnitude of errors. Do you know how to do it? Run the same program several time and see the fluctuation of the corresponding energy and state? What do you suggest?
best, Gang